I’m a masking tape guy, myself… Hard or soft edge on the demarcation lines can be done with the tape. For feathered edges, simply fold the tape back on itself for about a 16th-inch. This keeps the edge of the tape from sticking down tight and it produces a “soft” edge. For the canopies, I’m a free-hand painter in most cases, however I do mask occasionally… For free-handing, I mask one or two frames along each edge, paint it with a brush, then remove the mask, repeating the process until the canopy is painted. I don’t let the paint dry, either. the quicker masking tape comes off, the easier it is to remove, and any raised edges that are there will settle back down…
I’ve also used thin strips of tape, cut to the width of the framework, and lay it down over the frames, then mask the entire canopy with rubber cement. Once the rubber cement is dry, I rock (not slice) a knife-blade along the edge of the the tape, then peel off the tape and shoot the canopy. After the paint is dry, I remove the cement by rubbing it off with my thumb. This method works best for me on “bubble” or “blown”-type canopies… It’s also a good way for simulating paint-chipping. Simply paint the metallic in the area you want it, dab the rubber on it in a stabbing, stippling motion, let dry, and paint. Then when the paint’s dry, rub the cement off, exposing the metallic under it…
I’ve tried other liquid masking agents, but always went back to the old school rubber cement… Rubber cement’s cheaper too, by far…
For painting aircraft, generally I paint the cockpit and fuselage interior, engine(s), wheel-wells, and all that stuff inside prior to assembly. Once assembled and all the required fillig and sanding is done, I then paint the outside of the aircraft, masking the cockpits and wheel-wells with damp tissue stuffed in them (or sometimes I use rubber cement to attach the masked canopies and windscreens, strut covers, and doors to paint them as a unit, and to utilize them as masks… Props, tires, spinners, guns, ordnance, and the like get painted separately and attached during final assembly with CA glue, since generally, I don’t care to do a bunch of scraping to get the paint off those parts and their attachment points…
That’s just a general guideline, each model is different and requires a little paint-planning…